Is it fine to connect a load to the Drain of a p-channel JFET ?

Thread Starter

eCaleb

Joined Feb 11, 2022
20
I've noticed most simple circuits illustrated online to show how p-channel JFET works don't have the load connected to the Drain but to the source ?
 

Ian0

Joined Aug 7, 2020
5,082
If your circuit shows the load between a terminal of the JFET and the negative supply, then it IS connected to the drain.
 

Thread Starter

eCaleb

Joined Feb 11, 2022
20
If your circuit shows the load between a terminal of the JFET and the negative supply, then it IS connected to the drain.
If your circuit shows the load between a terminal of the JFET and the negative supply, then it IS connected to the drain.
Thanks, load do appear to be connected between one pin of the P-jfet and the positive supply, and I guess the JFET pin to which the load is connected is the source.
 

Ian0

Joined Aug 7, 2020
5,082
Are you sure it's a P-channel FET? You haven't posted the circuit diagram yet.
I could be a source-follower circuit, but it's quite unusual to make one with a P-channel device.
 

Thread Starter

eCaleb

Joined Feb 11, 2022
20
Are you sure it's a P-channel FET? You haven't posted the circuit diagram yet.
I could be a source-follower circuit, but it's quite unusual to make one with a P-channel device.

Consider the simple circuit below .

Source : learningaboutelectronic.com website .
 

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Ian0

Joined Aug 7, 2020
5,082
Indeed you are correct - a P-channel source-follower. Unusual.
The gain is marginally less than unity, and the output voltage is lower than the input voltage.
I would have expected the input signal to be referred to the positive supply, not the negative.
 

Ramussons

Joined May 3, 2013
1,262
I've noticed most simple circuits illustrated online to show how p-channel JFET works don't have the load connected to the Drain but to the source ?
This is a Common Drain configuration (like the common Collector in BJT). Voltage gain is Unity, but Current Gain is High.
It may be a bit confusing because it is shown Upside down.:confused:
 

MisterBill2

Joined Jan 23, 2018
11,876
Loads can be connected either on the drain side or on the source side, but the gate drive circuits will need to be a bit different. Understand that the control of the current is depending on the gate to source voltage, which must be controlled by the gate drive circuit. So the gate drive arrangement for a Source side load is different from how the gate is driven when the load is on the Drain side.
 

Thread Starter

eCaleb

Joined Feb 11, 2022
20
Thank you all for your respective answers, your contributions sincerely appreciated. Joined couple of days ago, I'm glad to be a member.
 
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