- This topic has 4 replies, 3 voices, and was last updated 1 month ago by LectronFan.
March 29, 2020 at 12:22 #8529LectronFanModerator
The 1007 digital Lectron lab has many cool blocks including a MOSFET module which is made around quite an old chip : the CD4007.
This chip has 3 N channel MOSFETS and 3 P channel MOSFETS.
These 6 transistors are matched and have the same properties.
The 1007 manual has a comprehensive and detailed description of this chip.
There are many circuits which describe the input and output characteristics.
It goes also in great detail about the output behaviour of a MOSFET, by performing some experiments, you learn how they sink or source current. Between Drain and Source, there’s always a resistance present and the voltage drop across this resistor can be measured.
When performing these experiments you are invited to take measurements and plot a graph.
These are real great experiments and you can learn a lot of them.
This is the best way to learn how MOSFETS in the CD4000 range behave.
It is clear that the author, Mr Kopperschmidt, did a marvellous job rewriting the whole digital lab (in comparison with the Legacy 300 system). The how and why are well explained with some formulas to make this easy to understand. The 1007 set is a true marvel and the manual has a great learning curve.
As an example, let’s try experiment 29 : a NAND gate build around this MOSFET module.
The original circuit shows the output with a meter and the manual mentions the use of a led cube.
But to make it even more “old school”, we can use an emitter follower which drives a lamp.
This emitter follower is also well explained in an earlier section of the manual. And now some questions for you :
– Why don’t we use a resistor at the base of the NPN transistor ?
– How large is the current flowing into the base ?
Here is the picture for you to enjoy :
- This topic was modified 2 months ago by LectronFan. Reason: Adding text
- This topic was modified 2 months ago by LectronFan. Reason: Typing error
May 2, 2020 at 17:34 #8600bodgerParticipant
That’s clever, I like it! I’m guessing that the base current to the bipolar transistor is limited by the channel resistance of the MOSFETs in the 4007, but I’m not sure what their on-resistance is.
May 2, 2020 at 17:36 #8607mwpeters75Keymaster
Thanks very much for joining the conversation! You are always welcome.
May 2, 2020 at 17:38 #8608mwpeters75Keymaster
As usual, very engaging analysis and presentation. I am going to send a copy of your post to Mr. Kopperschmidt, I am sure he will be pleased to read your comments.
May 3, 2020 at 07:47 #8617LectronFanModerator
Indeed Bodger, the Mosfet array has a certain ON and also OFF resistance. Typically, this lies around 400 Ohm.
Mr. Kopperschmidt described very well in the manual how the currents flowing through the Mosfet module can be measured by using the meter.
He also described in great detail the imedance converter or emitter follower.
Mostly, these currents are enough to drive a led, but not enough for a light bulb.
When we use an emitter follower, the current is amplified.
By the way, most emitter followers don’t need a base current limiting resistor. It all depends on the load connected at the emitter.
That’s also a the same emitter follower used in the Lectron legacy 300 set (image from the comprehensive Lectron blocks list by Mr. Günther Stabe)
This block uses the (old) PNP Germanium transistor and + as ground.
Do you think we can use this block in our circuit ?
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