Low-current, momentary action pushbutton switches, such as PCB-mount ‘tactile’ types, are cheap, and available in an abundance of different styles. Latching types, on the other hand, are often larger, more expensive, and available only in a relatively limited range of styles. This can be a problem if you need a small, inexpensive switch for latching power to a load. The solution is to convert a pushbutton’s momentary action into a latching function.
Previous Design Ideas have proposed solutions based on discrete components (Ref. 1) and IC-based circuits (Ref.2 and Ref.3). The circuit outlined below, however, requires just two transistors and a handful of passive components to achieve the same result.
The circuit in Figure 1(a) is configured to latch power to a low-side (ground-referred) load. It works in ‘toggle’ mode; that is, the first switch closure applies power to the load, the second removes power, and so on.
Figure 1 Circuit converts momentary action push switch into latching power switch.
To understand how the circuit operates, assume that the DC power supply, +VS , has just been applied, capacitor C1 is initially uncharged, and Q1 is off. The P-channel MOSFET, Q2, is held in its off state by R1 and R3, which work in series to pull the gate up to +VS , such that VGS is zero. The circuit is now in its ‘unlatched’ state, where the load voltage, VL , at the OUT (+) terminal is zero.
If the normally-open push switch is momentarily closed, C1 – being uncharged – pulls Q2’s gate to 0V, thus turning on the MOSFET. The load voltage at OUT (+) now rises immediately toward +VS , and Q1 receives base bias via R4 and turns on. Under these conditions, Q1 saturates and pulls Q2’s gate low via R3, thus holding the MOSFET on when the switch has opened. The circuit is now in its ‘latched’ state, where both transistors are on, the load is energized, and C1 charges up to +VS via R2.
When the switch is momentarily closed for a second time, the voltage on C1 (by now approximately equal to +VS ) is transferred to Q2’s gate. Since Q2’s gate-source voltage is now roughly zero, the MOSFET turns off and the load voltage falls to zero. Q1’s base-emitter voltage also falls to zero and the transistor turns off. Therefore, when the switch is released, there is nothing to hold Q2 on, and the circuit reverts to its ‘unlatched’ state, where both transistors are off, the load is de-energized, and C1 discharges via R2.
Resistor R5 across the output terminals is an optional component that acts as a pull-down. When the switch is released, C1 discharges via R2 into the load. If the load impedance is very high (i.e., similar in magnitude to R2), or if it contains active devices such as LEDs, the load voltage at the instant Q2 turns off may be large enough to bias Q1 on via R4, thereby preventing the circuit from turning off properly. The presence of R5 pulls the OUT (+) terminal down to 0V when Q2 turns off, thus ensuring that Q1 turns off rapidly, and allowing the circuit to revert to its unlatched state in a proper manner.
Provided the transistors are correctly rated, the circuit will work over a wide voltage range and is well suited to driving loads such as relays, solenoids, LEDs, and so on. However, beware that certain DC fans and motors continue to rotate when their drive power is removed. This rotation can generate an EMF large enough to bias Q1 on, thereby preventing the circuit from switching off. You can eliminate this problem by inserting a blocking diode in series with the output, as shown in Figure 1(b) . You must also include R5 to ensure Q1 turns off properly.
The complementary circuit outlined in Figure 2 is intended for ‘high-side’ loads connected to the positive supply rail such as the relay shown in this example.
Figure 2 Complementary circuit intended for high-side loads.
Note that Q1 has been replaced with a PNP transistor, and Q2 is now an N-channel MOSFET. The circuit operates in a similar way to the one described above. Here, R5 acts as a pull-up resistor which pulls the OUT (-) terminal up to +VS when Q2 turns off, thus ensuring that Q1 turns off quickly. As in the previous circuit, R5 is optional and only necessary for the types of load mentioned previously.
Note that in both circuits, the time constant produced by C1-R2 provides for debouncing of the push switch contacts. Normally, a value of 0.25s to 0.5s should be adequate. Smaller time constants may lead to erratic behaviour, whereas a larger time constant increases the waiting time between switch closures necessary to ensure that C1 charges and discharges properly. With C1 = 330nF and R2 = 1MΩ as shown, the time constant is nominally 0.33s. This is usually sufficient to debounce the contacts and to allow the load power to be toggled after a couple of seconds or so.
Both circuits are intended to latch and unlatch in response to brief, momentaryswitch closures. However, they have each been designed to ensure correct operation even if the push switch is held closed for any length of time. Consider the circuit in Figure 2 when Q2 is on. When the switch is pressed to unlatch the circuit, the gate is pulled down toward 0V (since C1 is uncharged) and the MOSFET switches off, allowing the junction of R1-R2 to rise toward +VS via R5 and the load impedance. At the same time, Q1 also switches off, such that Q2’s gate is pulled to 0V via the series combination of R3 & R4. If the switch is released immediately, C1 will simply charge up toward +VS via R2. However, if the switch is kept closed, Q2’s gate voltage will be defined by the potential divider formed mainly by R2 and R3+R4. If we assume that the OUT (-) terminal is roughly equal to +VS when the circuit is unlatched, Q2’s gate-source voltage is given by: VGS = (+VS ) × (R3 + R4)/(R2 + R3 + R4) = 0.02(+VS ). Even if +VS is as high as 30V, the resulting gate-source voltage of around 0.6V will be too low to switch the MOSFET on again. Consequently, both transistors remain off until the switch contacts open.
The circuit in Figure 2 is latched on by momentarilyclosing the push switch when C1 has charged up to +VS , which causes OUT (-) to drop to 0V as Q2 immediately turns on, rapidly followed by Q1. A momentary switch closure would allow C1 to discharge to zero via R2 after the contacts open. However, if the switch is held closed, Q2’s gate voltage will be defined by the potential divider formed by R2 and R3. Since Q1 is saturated, the junction of R3-R4 at Q1’s collector will be pulled up to +VS , and the junction of R1-R2 will be pulled down to 0V via Q2. Therefore, with the switch held closed, Q2’s gate-source voltage is given by: VGS = (+VS ) × R2/(R2 + R3) = 0.99(+VS ). Consequently, provided the supply voltage is at least equal to Q2’s gate-source threshold voltage, both Q2 and Q1 will remain on until the switch contacts open.
Both circuits provide an inexpensive way of deriving a latching function from a momentary switch and, just like a mechanical latching switch, the quiescent (unlatched) power dissipation is zero.
Read the next Design Idea in this series : A new and improved latching power switch
This is a brilliantly simple circuit. Is it also low cost? Im having trouble finding an ideal low cost Q2 component for small LED circuit. Anyone got a suggestion? Could/should Q2 be replaced with a BJT ? I note the PDF download has Hartley Smith as the de
Hi Simon, As author of this Design Idea, I'd like to thank you for your kind comments. As to my name on the PDF download, my user name is HartleySmith, so I suspect that the web author has mixed up my real name and my user name. For many applications, it s
I must say that I have been searching for about two months for a circuit that is simple and does the job for me and this is the one that worked from the beginning. I have built much more complicated circuits and none worked. I could not be happier. I use it to control photo cells that turn off my microphone going to my mixer from across the room. If anyone is interested in my complete circuit just write to computerlen at hotmail.com. I do not use relays because they were causing a minor ‘click’ sound when switched on and off. Thank you very much. Len.
Many thanks for your kind words. It’s not often I get such positive feedback! I’m delighted that my circuit has solved your problem. Best wishes, Anthony H. Smith
“Hi AnthonynnOf the three circuits I have tested this one works the best for my purpose. One did not work (but lets say I made a mistake in the wiring that I could not find) and another was ON when powers was connected. I needed a switch that is OFF when
“If you are using the high side(ground switched) one you should be able to connect an NPN collector to the positive rail with its base to the load negative(it will be pulled high via resistor R5). The emitter can then be connected to the led and then its c
“Hi Anthony,nI would also like to thank you for this wonderful simple circuit. It's been years since I dabbled with analog circuits but have a need to get back into them now and your circuits are perfect for my needs.nI have built your second high-sided
“Hi Tfboy,nThanks for your comments. I'm glad you like the circuits.nIf you need a CMOS logic output, it may be possible to use the Fig.2 circuit and connect the output at Q2's drain to a suitable logic gate. A Schmitt trigger device such as a 74HC14 (or
“Hi Anthony,nThanks for the reply – I hadn't noticed it before. Much appreciated.nYes, I did consider SR / JK circuits, but as yours included the debouncing side, I found it a more elegant solution for my needs, particularly with the adjustable debounci
“Thanks Anthony for this excellent and creative circuit.nJust wondering, if I wanted to control the switching with a microcontroller (eg Arduino), ncould I replace the push switch with a transistor (eg N channel MOSFET) and connect a digital output pin o
“Hi Anthony, nnThanks for posting this design. I was playing around with the circuit on a breadboard for hobby purposes. I powered it with a 12V supply and tried a variety of p-channel mosfets. For all of them, when I initially connected power, my load (
“Hi Anthony,nnLove the design. I was wondering if you had any ideas for how I can utilize the first design but instead of having power on when the circuit is powered up I' like the output to be in an off state. nnThanks!nGreg”
“nHi Nukemaster I like your idea but was hoping to clarify. Please let me know if this is incorrect. The NPN collector goes to positive rail, base to out(-), LED + resistor to board GND.nnThanks!”
“Hi GeorgeG404,nSorry for the delay in getting back to you.nIf you wanted to control the circuit of Fig.1 with a microcontroller port, the simplest way would be as follows:n(1) Dispense with the push switch, C1 and R2. n(2) Combine R1 and R3 into a sin
“Hi Anthony,nThe first circuit is almost exactly what I'm looking for and the explanation is really appreciated. Is there a way to replace the mechanical switch with a Hall sensor? The Honeywell SL353LT.nThe supply voltage of the Hall sensor is 2.2v to
“Hi Davidk,nThe circuit as it stands was designed to be used with a simple, momentary pushswitch having volt-free contacts, so I think you may have problems interfacing it to the SL353LT Hall sensor. I don't have a sample of the SL353LT, but the datasheet
“Thanks,nnI used the circuit in figure 1 using an IRF9540N and a BC547 on a breadboard with and LED. When I turn on the 9v power supply the LED randomly starts in ON or OFF state. The switches work and turns on/off the led. Is this due to the type of m
“I soldered this on a vero board and it works great now!”
“Hi Anthony,nHow about if I wanted to use the switch and the micro port like a two way switch?nSo turn on with button and off with micro port, or visa versanRegards,nDean White”
“Hi AnthonynnThanks for the circuit I am looking for. Is there a chance to get rid of the current flowing through R1 (Fig 1), when the circuit is on?nnThanks a lot.nn-urs”
“Hi Mcbain1,nThere is no easy way to eliminate, completely, the current flowing through R1 when the circuit is latched on. However, you can minimise the current by increasing the value of R1. The circuit shows a value of 10k, but you could increase this b
“Hi, since I'm new to MOSFETs, would you all please mind to help me in choosing a cheap and compatible MOSFET for this circuit……Also, try to name some readily available MOSFETs please.”
“Hi: I'm a relative beginner at IC circuits. I have a series of existing wall lights that I am planning to convert to two different lamps in each fixture (One for an LED candle effect & the other for LED spotlights.) Can anyone show mw a circuit that wi
“Hi Anthony, do you think i can use this schema to trigger on an usb device? i want to have choice to manually activated an usb device, right now one way i found is this device:nhttps://media.digikey.com/pdf/Data%20Sheets/Adafruit%20PDFs/1400_Web.pd
“Hi Anthony,nterrific website.ni am an auto mechanic in Australia (with very grey hair).nobviously i have little knowledge of electronics, but i have a job putting a foot operated headlight dimmer switch in a ford focus 2011.nthe column stalk is a mome
“Hey, nFor Q1 you can use any general purpose transistor like BC458 or 2N2222 and for Q2 you can use FQP27P06 P-channel MOSFET. “
“Hey, nFor Q1 you can use any general purpose transistor like BC458 or 2N2222 and for Q2 you can use FQP27P06 P-channel MOSFET. “
“I stumbled upon here while searching in general for this stuff. I must admit I was, at first, going to use a standard side switch in series with a resistor to drive an n-channel MOSFET gate and be done with it, but this looks really cool, and I happen to
“Hi Barkuti,nGlad you like the circuit – it's really great to get such positive comments.nYou are right about the values of C1 and R2. The values are not critical and you should be able to experiment with different values to get the best performance for
“Hello Anthony, I am looking for a circuit like this to power up a class D amplifier. It will need to switch 40-48Vdc 8amps. Can you suggest a MOSFET for this?”
“Hi,nWill you be using the circuit in Fig.1 or Fig.2?nAlso, do you intend to use a conventional (through-hole) device, or a surface-mount MOSFET? Do you have a tight budget for the device, or is cost not too much of an issue?nCheers,nAnthony H. Smith”
“this looks awesome! i was wondering if you could help me though. im trying to take this and make it work for some guitar pedals im building, im using momentary 3pdt switches and im also using a 2 way toggle to turn the latching feature on and off. any inf
“Hi Andrew,nSo long as the transistors are properly rated to handle the voltages and currents in your design, I would think the circuit would be well suited to controlling a guitar effects pedal. However, bear in mind that the idea is effectively a latchi
“Hi AnthonynGreat circuit.nIu2019m thinking of using 2 of these with steering wheel mounted buttons for turn signal on my kit car.nDo you think they would work? And if so, can you suggest how I wire up the switches so that a press of the left button wi
“Hi Hartley, This look like a great solution. Soon as I get the parts will try it out. Can I ask how you would adapt the Figure 2 diagram to work with a micro controller, say an ATtiny13 running at 4V or so?”
“Ok, got the parts and tested it out. Works great. Connected the ATtiny to Q1 via resistor to pull it high when it needs to turn off. Thanks again for a great design.”
“Hi Bunder444,nMany thanks for your comments. I'm delighted that the circuit works well with your ATtiny. Good luck with your project.nCheers,nAnthony H. Smith.n”
“Hello Moose,nAs long as the circuit components are properly rated for the voltage and current levels in your application I think the circuit should be well suited to controlling your turn signals. I am assuming that you have some kind of astable circuits
“made it and is working perfectly well. Min. Power required is 5v for irf9450.nI was wondering if we can modify the circuit to have time based OFF…baby does not sleeps when it is dark …so a 30 min timer will help her to sleep and lights out”
“Hello Anthony, I have this circuit on a breadboard with a PN2222 for the NPN transistor and a NTD2955 for the P-Channel Mosfet. The circuit works to toggle power. There is one thing that puzzles me. If it is on when I remove power, even if I short the cap
“Since I am not so good in electronic formulas and others, Wish to know which P Channel MOSFET to select for input of 3.7 V to Output 3.7 ? This output will go to Buck boost circuit which will give 5V outputnnI also wish to use ATTiny with Timer to switc
“Can you please more details on connections please and also which Circuit P Channel or N Channel is used to connect ATTiny”
“When selecting the appropriate P-Channel MOSFET, first use a parametric search for Vgs Theshold. This is the voltage difference between the source (V+) and the gate (gnd) and the potential when MOSFET starts to pass current to the drain (load). This will
“For example, reading the graph on page 4 of the datasheet for LP0701, it will pass about 1 amp at a Vgs of 3.5. However, you want to confirm all properties of this MOSFET will work for your application. Vgs and Id are negative values only because it's a P
“HI Anthony, thank so much for the design and write up. Am I wrong or could a simple NPN transistor work in place of the MOSFET in fig. 2? Or is the N-channel FET necessary? I'm just looking at them as simple switches. nnFor a momentary switch that is no
“Hi Anthony, thanks for the design! I used it to control an LED project and ran into the problem described where it would switch on but not off; a smaller value for R5 fixed it. But I don't follow what was happening in this case, please could you go into m
“Nice circuit, worked the first try (2N3904 & ZVP3306A). However, the start-up state varies. Mostly it starts up in the ON state when it is connected to battery. Sometimes it starts up in the OFF state when connected to the battery. Been playing with c
“I have a 3d printer, it has a raspberry pi and RAMPS board. Standard 12v power supply. The power inlet has a switch. I would like to use a momentary push button to turn off/on/ the ramps board and a dc/dc converter powering the pi. Could this circuit d
“I would be using fig1, itu2019s just 12v”
“Hi, Thank you for sharing your idea.nI also working with push on/off circuit for long time. Today I finally made almost perfect circuit.n- 3v ~70v wide voltage rangen- Zero current consuming at standbyn- Very stable.n- No power on at battery connect
“A late replay but if you are still working on this it may be worth looking at. The on state is set by the current through the base of Q1 which is very tiny. If a resistor is added from the base of Q to Vcc, it is better controlled as a voltage level sets
We set up circuit Figure 1 but we don’t get it working Its continue ON mode.
For Q2 we use SI2301 A1SHB SOT23 P-CH MOSFET. For Q1 we use BC847Transistors Bipolar NPN.
We don’t get it working Its continue ON mode.
Hi Alpesh, The devices you have selected are good choices, so I do not see why the circuit in Fig.1 shouldn’t work. Recheck all your connections and remember that Q2’s gate is very sensitive – breadboarding can sometimes lead to noise and leakage currents that can upset the operation of MOSFETs. Also, try fitting R5 if you don’t currently have it in circuit. It can help to pull down Q1’s base and thus make sure it turns off properly. Good luck, Anthony.
Still, we have no success.
We have on board design based on the KiCad tool and we have PCB from JLCPCB.
Can you guide me about the Cn=330nF capacitor its SMD we use it SMD 0805 Ceramic package is that issue?? Can we use 100nF ??
We also change that with tantalum 10uF as well as 10uF Ceramic cap but no success.
Still, we have no success.
We have on board design based on the KiCad tool and we have PCB from JLCPCB.
Can you guide me about the Cn=330nF capacitor its SMD we use it SMD 0805 Ceramic package is that issue?? Can we use 100nF ??
We also change that with tantalum 10uF as well as 10uF Ceramic cap but no success.
We got some result when we power up its OFF but when we push button single time its ON and then continue ON after that no work as push ON OFF can you guide me what is issue?
What a joke. All the old comments have been truncated. Was the new site not tested at all?
For figure 1 design as we test
For figure 1 design as we test
For Q2 we use SI2301 A1SHB SOT23 P-CH MOSFET. For Q1 we use BC847Transistors Bipolar NPN. For C1 we use SMD 0805 Ceramic Cap (Not a mention in the post its Tantalum polarized or Ceramic is better)
Design is working fine first stage I mean when we supply load voltage is zero but when we press switch single time we get continue load voltage and no change stage so please can you confirm what is wrong or we get not latching.
Can you tell me exactly what kind of load are you driving?
We use LiPo 3.7V Battey as a power source to this circuit and as a load use Buck Regulator 3V to run a 3V LED.
Would I be correct in assuming that there is a fairly large capacitor at the input to the buck regulator?
Mr. Smith, i faced the issue with your circuit just like it was reported above – it mainly has reversed initial state – Vs on output with initial power on. It’s not a big issue actually, issue is – this state fluctuates. It may be 0 or Vs as power is on. I made simulations with software, it shows that both gate and drain voltage rises on power on, and then, about 4V on Drain and 2V on Gate it makes nike’s swoosh. Then voltage on Gate drops to 0 (green) and MOSFET opens fully (brown) – check the pic: https://wmpics.pics/di-Z2Q6.png
i guess MOSFET can’t reach gate cut-off voltage before Q1 opens and prevent it closing. Any comments? Suggestions? P-Mosfet is IRLML9303, NPN – BC847C. Vs – 5 Volts, the rest same as at your circuit.
Solution was found as using NPN transistor with lowest gain current coefficient you can find. h21 = 20..40 should be OK
This circuit does not work as presented in fig.1 Under simulation problems as described by replies above are evident. Does the author simulate and/or build his designs? Some other posts of his suggests he does, evidently not this one tho. Some tweaking is required. I have added a cap from Q1 base to 0V to ensure Q1 is off at startup. A value of 100n should do. The value of R1 has to be reduced to approx 300ohms to ensure Q2 turns off at the second button press. See the LTspice circuit and graphs here https://imgur.com/9WCPWP6
This looks perfect for what I want to do. I am using (2) 5v relays, each drawing 72ma (144 ma total) at 5V for the load. From your description, I think I need a P-channel (depletion) MOSFET, but NTE is only showing me P Channel (Enhancement) MOSFETS. Am I mistaken? Or do I need an N – type MOSFET. I am a newbie, apologies — I am going to need the negative to be directly connected to the load, while Vs is switched. I am using figure 1 in your article. Can I use BC547 for Q1? Any help in selecting the proper Q1 and Q2 components would be very much appreciated. Thank, Brin
No need to apologise for being a newbie (we were all newbies once).
If you intend using the circuit in Fig.1, you will need a P-channel enhancement MOSFET for Q2. If your total load current is 144mA, I would recommend a device with a drain current rating of at least 200mA. Assuming you intend powering your circuit from 5V, I would suggest a drain-source voltage rating of at least 8V. You should be able to find plenty of MOSFETs that are suitable.
A BC547 NPN transistor should be fine for Q1.
You will need a back-EMF protection diode for your relays such as the one shown across the relay in Fig.2. Some relays are provided with protection diodes already fitted across their coils. If your relays are like this, then you must connect the anode terminal of the relays to OUT(-) and the cathode terminal to OUT(+).
If your relays do not have internal diodes, you must fit one yourself across the circuit’s output terminals. The diode’s anode must be connected to OUT(-) and the cathode to OUT(+). A diode like the 1N4001 would be suitable.
Hi, I am trying to repair a board that has a similar on / off system.
Looking and taking some measurements I have reached the following diagram. As I have no experience in these systems, it is difficult for me to know if it is okay.
In particular with capacitors 3 and 4. I appreciate any comments, greetings!
I’m curious as to why you use a mix of bipolar transistor and MOSFET in this circuit. Did you have a particular reason for choosing a bipolar transistor for Q1? I am thinking of using a circuit like this but with a MOSFET for Q1, possibly dispensing with R4. Is there anything I am missing?
Using a bipolar for Q1 is inexpensive. Also, having a fairly well defined switching threshold (which is simply the Vbe) results in a reasonably predictable and adequate time constant for the C1-R2-R4 network (Fig.1).
You could certainly try a MOSFET, but there are two issues to consider. First, the switching threshold now becomes the Vgs(th) of the device. For a typical device like the 2N7000, this can vary from 1V to 3V which is a much wider spread than the bipolar’s Vbe (typically 600mV – 700mV). This could lead to a correspondingly wide spread in the time constant which might lead to unpredictable or erratic behaviour. Second, since Vgs(th) could be quite large, it could limit the lower operating voltage of the circuit although this caveat would, of course, also apply to the MOSFET used for Q2. Naturally, you could use a low-Vgs(th) MOSFET for Q1, but again this is likely to be more expensive than using a common-or-garden bipolar. A good thing about using a MOSFET is that it would eliminate effects caused by the bipolar’s base current, although in tests I never found this to be a problem.
As the circuit is intended to be a design idea (not a rigid template) there are many other ways you could implement it. For example, Q2 (Fig.1) could be a bipolar device, or even a Darlington. The optimum device types and values will depend on several factors (supply voltage, load current, cost, etc.) and you would have to decide on what’s best for your intended application.
Have you tried a MOSFET for Q1? If not, please do so and let us know how you get on.
Does fig 1 gives exact output as DC supply without any voltage drop? When simulating the circuit, there is 0.8v drop in output .
I am using 7.4 as dc supply, Will I get same 7.4 in the output in both high-side and low-side drive circuit?
In fig 2 circuit. The circuit is latching but it is not de-latching on next press. Please help me out. N-channel mosfet gate voltage remains high,it does get low on second press.Is is a problem with pnp/capacitor? Please help me to sort this out.
In fig 2 circuit. The circuit is latching but it is not de-latching happening properly, I have to press 3/4 times to to de-latch. What could be the reason?
Ok, after coupling more loads to the DC motor, I am able to switch of the supply. Still sometimes it doesn’t switch off. I have to hold to shaft and press to switch off. I have a blocking diode in series and diode in parallel as shown in fig2. Do I need to give a couple of seconds interval between on and off?Please help to perform smooth operation
Thank you for graciously sharing your expertise, time and effort!
I have built the Figure #2 circuit. I am using a 2N3906 P-BJT for Q1 and a 2SK2232 N-MFET for Q2; Vgs(th) = 4V max. Vsupply is 5V. The Load is a Green LED with 1K resistor. R5 is in place. I am using a 330uF/334 ceramic cap, as the schematic does not indicate an electrolytic cap.
The circuit will not latch. The Load LED simply blinks a single blink = on/off.
I have tried removing R5, varying the capacitor value and holding the button down for a longer period.
I am experienced with bread boarding. All connections were verified against the schematic and each connection verified point-to-point with a DMM, before the first power-up. So, a wiring error, or open circuit, seems less likely. (But, I humbly recognize that either is possible.)
I will continue to work with the circuit. But, in the meantime, what might you suggest that I try?
Where is your 330uF cap located?
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