chopper A need help urgent

[bbexpress]

lm358 driving power mosfet

I need help to finish this project. I used 2 IC555 as Astable and Monostable to trigger the MOSFET IRF620 n channel, I can also change the frequency and duty cycle.
I got two problems.
1/. The output signal is small when compare with input voltage(~50V), can the LM358 amplify this signal, if not, what else IC I can do, I know 7667 can do, but my chip is broken.
2/.I can not wire the MOSFET. Say, the Gate is trigger, the Drain and Source is confuse me....the freewheeling diode connect between the Drain and what.....and where the load go....please help me to wire this in more detail or schematic with detail information.
appreciate your help.

 

[nicleo]

lm555 trigger for mosfet

I need help to finish this project. I used 2 IC555 as Astable and Monostable to trigger the MOSFET IRF620 n channel, I can also change the frequency and duty cycle.
I got two problems.
1/. The output signal is small when compare with input voltage(~50V), can the LM358 amplify this signal, if not, what else IC I can do, I know 7667 can do, but my chip is broken.
2/.I can not wire the MOSFET. Say, the Gate is trigger, the Drain and Source is confuse me....the freewheeling diode connect between the Drain and what.....and where the load go....please help me to wire this in more detail or schematic with detail information.

You do not need extra freewheeling diode connected across Drain and Source because IRF620 already has an 'embedded' diode as shown in Figure 1.

Added later:
Err ... I guess you mean the freewheeling diode across the load (should be inductive load). If that's the case, you should connect as shown in Figure 2.

By the way, I do not quite get your point in Question (1). Do you mind to elaborate more? Thanks.

 

[bbexpress]

chopper lm555

I have a schematic which I'm doing right now, but something is wrong with the connection. Say, Vcc has to connect with the Cathod of Diode, and Anode connect with Drain, Source is ground, the output is between freewheeling diode...but I get the output just around .4V with input around 50V....that's my problem.

 

[nicleo]

I have a schematic which I'm doing right now, but something is wrong with the connection. Say, Vcc has to connect with the Cathod of Diode, and Anode connect with Drain, Source is ground, the output is between freewheeling diode...but I get the output just around .4V with input around 50V....that's my problem.

The connection in the schematic is OK. In the schematic, you configure the mosfet as high-side switch. To make the mosfet operates correctly, proper gate driving circuit is required (e.g. high-side mosfet driver IC). Do you mind to explain the driving circuit of the mosfet?

 

[bbexpress]

Yes. Actually, I built the circuit exactly you posted, but the output is so small, can not drive the power resistor and inductor.
The driving circuit I built I used the schematic LM555 National Semiconductor as Figure 4 and Figure 1 to trigger the Mosfet. The output from Figure 1 is low, I used 7667 chip to amplify the output signal, it works before but I got short one time, and it's dead now.....
Without using 7667, I just got around 0.4V output, it's not enough to drive the power resistor....
The schematic I posted is from the lecture, I built the circuit like you post here.
thanks

 

[nicleo]

Yes. Actually, I built the circuit exactly you posted, but the output is so small, can not drive the power resistor and inductor.
The driving circuit I built I used the schematic LM555 National Semiconductor as Figure 4 and Figure 1 to trigger the Mosfet. The output from Figure 1 is low, I used 7667 chip to amplify the output signal, it works before but I got short one time, and it's dead now.....
Without using 7667, I just got around 0.4V output, it's not enough to drive the power resistor....
The schematic I posted is from the lecture, I built the circuit like you post here.
thanks

Sorry to ask this ... Is the power supply to ICL7667 (is it ICL7667?) correct, i.e. 15V or less? Besides, what is the frequency of the signal generated by the 555 circuit?

 

[bbexpress]

i used this chip
**broken link removed**
but other country make it, they called 7667,input is pin2, pin 2 connect with pin 3 by one resistor, pin 3 also go to ground, pin 6 go to Vcc, pin 7 is output to trigger the mosfet....can i replace this chip by LM358, it's just amplifier the signal....i forgot the frequency, but i used R~3k, C=0.01uF.

 

[nicleo]

... can i replace this chip by LM358, it's just amplifier the signal....i forgot the frequency, but i used R~3k, C=0.01uF.

In your first post, you suggested to replace the ICL7667 with LM358. In my opinion, the output current of LM358 (i.e. 20mA maximum) is not enough to drive a 6A/200V power mosfet IRF620.

 

[bbexpress]

so, how come I can increase the output voltage, any other ways....It's so low, I can not drive the power resistor...thanks

 

[IanP]

Check better your 555. Its output should easily drive power mosfet. It should be able to sink and soure currents of up to 200mA.
I don't think you need an amplifier for this purpose...

 

[nicleo]

I have a schematic which I'm doing right now, but something is wrong with the connection. Say, Vcc has to connect with the Cathod of Diode, and Anode connect with Drain, Source is ground, the output is between freewheeling diode...but I get the output just around .4V with input around 50V....that's my problem.

If the output (voltage across load or freewheeling diode) is 0.4V only, then the mosfet is not driven correctly.

so, how come I can increase the output voltage, any other ways....It's so low, I can not drive the power resistor...thanks

Let the 555 circuit alone, i.e. without connected to mosfet. What's the VCC to the 555 IC ( pin-8 )? Power on the 555 circuit, what is the output voltage (amplitude) at pin-3 ? If the VCC is 15V, the output voltage should be close to 12.5V or more dependent on the load current. Pls update us. Thanks.

 

[VVV]

First of all, what load is it?
If it can take the entire input voltage, try to drive the mosfet directly from the 555 power, i.e. connect the gate through the resistor to the Vcc of the 555. Now you should see the entire voltage across the load. If you don't then the MOSFET is defective, or the 555 voltage is too low

Next, or if the first test is not possible, I would test the monostable/ astable with just an LED+resistor connected at its output. You should be able to see the LED brightness change. I hope you have the 555 running at a high enough voltage to be able to actually turn on the MOSFET.

Hope this helps.