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Can transistors replace this circuit

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johntee

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Hi guys, This may seem a somewhat naive request, but I'm just learning electronics. Can this circuit be changed to use semi conductors; preferably transistors because I have some of these? I need the output to swing alternatively from positive 27v to negative 27v when driven by the square input pulses, but doing away with the DPDT relay.

Thanks in advance

John
 

The circuit in the attched file perhaps can

realize your intent, but

it need two spuuly, one is 27V and the other

is -27V.


best regards




johntee said:
Hi guys, This may seem a somewhat naive request, but I'm just learning electronics. Can this circuit be changed to use semi conductors; preferably transistors because I have some of these? I need the output to swing alternatively from positive 27v to negative 27v when driven by the square input pulses, but doing away with the DPDT relay.

Thanks in advance

John
Click to expand...
 

    J

    johntee

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Thanks funster, I only have one battery supply of 27 volts and replacing the relay is my main task. I suppose if all else fails and I don't get any other feedback from the forum members I will have to adopt your suggestion.

Thanks again,

John
 

Some form of bridge circuit will work. An expensive way is opto couplers with resistive or FET controlled conductances. Another is a quad of jfets.
 

Why don't you use two 2x1 multiplexers, one having +27, -27 at 1 and 0 inputs and other having -27 and +27 at 1 and 0 inputs. The output of your two multiplexers will then provide you the necessary voltage swing you are looking for.

Added after 4 minutes:

funster said:
The circuit in the attched file perhaps can

realize your intent, but

it need two spuuly, one is 27V and the other

is -27V.


best regards
Click to expand...

This circuit will not give you a good +-27V swing. There will be drops in transistors as well as a lot will depend on the size of resistors.
 

You have only 27V in your circuit and what you would like to achieve is 54Vpp, so switching this 27V with a relay will not produce anything like on your drawing; switchng this relay will only change the poles and nothing else ..
What you really need is +/-27V (or a little bit more) supply and a couple of PNP (or P-channel Mosfet) and NPN (or N-channel Mosfet) transistors working as switches, and this can be accomplished in a full/half bridge configuration..
Regards,
IanP
 

    J

    johntee

    Points: 2
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Hi IanP,

This is the full circuit I got the above configuration from. Yes, the original does change the polarity each time the relay is activated by the 555 pulse. What I need is to maintain this same action, ie polarity changing, but I really need to do away with the relay to save on battery drain. I must tell you that I'm a real novice at elecronics so some suggestions without actual supporting schemetics go way above my head
 

I have attached a circuit with so called H-Bridge. It is based on 4 transistors: 2 x pnp (high) and 2 x npn (low), and it is controlled by 2 x 311 comparators. Thes comparators have 2 outputs (one of which is "open collector") so they can directly drive high and low transistors. The transistors are controlled in "pairs": one from high + one from low, and by switching these pairs you will achieve the same output as from a relay. Depending on the current you need to switch you can emplouy low power transistors (2N2222 as NPN and 2N3906 as PNP, or similar) or power darlingtons as on the picture..
If you need more info, come back..
Regards,
IanP
 

    J

    johntee

    Points: 2
    Helpful Answer Positive Rating
Hi IanP,

You have really excelled here, words of thanks seem inadequate, but many thanks anyway. I truly hope that I will be able to help others too when my knowledge of electronics develops.

Kindest regards,

John
 

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